The invention is concerned principally with apparatus whose primary use is in instrumentation, although not necessarily so. The apparatus of the invention is, in effect, a transducer of a mechanical type. Motion which is basically translative in a substantially linear path is converted into motion which is rotary by such apparatus.
The simple function stated above is one which can be performed by many well-known mechanisms such as, for example, a rack and pinion gear meshing. The invention herein, however, evolves from the application of the said simple function to a case where there are two requirements which are not readily met by the prior art. One requirement is that the conversion occur through a physical barrier such as a hermetically sealed wall and the other requirement is that the conversion occur in accordance with a predetermined relationship.
The first-mentioned requirement is basically capable of being achieved by the use of magnets moving on opposite sides of the wall and having their magnetic fields linking through the wall, but the second function is believed not to have been achieved by any prior art known with the benefits and advantages of the invention as demonstrated by the specification which is submitted herewith.
This invention is exemplified hereinafter by a novel pressure gauge of the type in which a fluid is caused to move a pressure responsive member, such as for example the flexible center of a suspended diaphragm, the gauge having means for transducing this movement into the rotation of a pointer indicator moving over a suitable dial that is calibrated to read pressure units. As will be deduced from the preliminary remarks of this background discussion, the invention is considered broader and applicable to any apparatus which can utilize the novel transductive mechanism thereof. In gauges and instruments, the mechanism can be used for measuring other parameters besides pressure. In manufacturing processes, the mechanism is capable of functioning as a control element in feedback systems, furnishing a needed error movement one way or the other relative to a norm pre-established for normal operating conditions. The mechanism can be used to record or transmit information concerning movement. Since the practical application of the invention has been to the construction of a pressure gauge, the discussion hereinafter primarily will be limited to the description of such gauge, but no limitations are intended thereby. As for the gauge itself, features are provided which are believed novel in and of themselves in combination with the transducing or converting mechanism and these will be pointed out and claimed.
Any gauge for measuring a parameter is intended for continuous and automatic use to obviate the need for manual measurements and calculations using classical techniques. Accuracy and reliability are the principal ends sought and the apparatus of the invention is intended to provide these attributes. The invention, however, achieves other advantages which give characteristices that have been sought in other gauges but not always achieved, certainly not all in any known gauges.
In the type of gauge described a variable parameter is represented by a rectilinear mechanical movement that is transduced into a rotary movement for the purpose of driving a pointer indicator. The particular type of gauge is ideally suited for conditions where the meter movement carrying the pointer indicator is preferred or required to be physically isolated from the mechanical movement that is being produced by variation of the parameter being measured. This would be, for example, the case where there are fluids in the measuring portion of the instrument which could damage the meter movement or impair its reliable and accurate operation.
The invention teaches the use of a magnetic coupling to accomplish the isolation above mentioned, such coupling enabling a frictionless transmission of energy from the measuring movement to the drive for the pointer indicator.
There are many known schemes for transmitting motion through magnetic coupling in instruments. Several examples are disclosed in U.S. Pat. Nos. 2,745,027, 2,722,617, 2,564,676, 2,371,511 and 2,260,516. These examples have disadvantages which are obviated by the invention. The invention contemplates a small array of two or more bar magnets which moves in a substantially rectilinear translation relative to a single rotary magnet. A small movement of the array can be arranged to produce a relatively great movement of the rotary magnet, the spacing between the array and the rotary magnet being generous considering the sizes of the magnets thus permitting the intervention of a pressure or liquid barrier. The side by side location of the bar magnets and their field interference with one another enable the formation of a composite magnetic field which can cooperate with the magnetic field of the rotary magnet in order to shape the field as desired and thereby to control the resulting relationship between the rectilinear and rotary movements. In other words the function represented by the angular rotation of the rotary magnet for any given rectilinear movement of the bar magnet array can be established as desired.
One important type of function that can be achieved is a linear function, this being useful in cases where the parameter being measured varies linearly. The scale over which the pointer indicator driven by the rotary magnet swings can thus be made with uniform divisions, enabling easy interpolation and extrapolation.
Another important type of function that can be built into an instrument constructed according to the invention is a second order function for use in measuring pressures which vary as the square root. The pointer indicator then is arranged to move approximately logarithmically for a given rectilinear movement of the array, this being accomplished by properly dimensioning and positioning the magnets. Again the scale over which the pointer indicator sweeps will have substantially equal divisions.
It is essential for a complete understanding and appreciation of the invention to comprehend the state of the art as contrasted with the advance which is represented by the basic concepts of the invention.
In the prior art, the above-mentioned patents being examples, the transfer or conversion of movement by means of magnetic fields has been represented primarily by those cases in which there is a pole to pole confrontation so that the movement of a magnet relative to another magnet or the movment of a series of magnets relative to one another is accomplished by the magnetic forces linking pole to pole. In all such cases, so far as we are aware, the movement is not much different from meshing gears or the coupling afforded by rotating the field of a synchronous electromagnetic device to achieve rotation.
In such structures as known the movement achieved and the demands upon the apparatus engender limitations which many instrument makers cannot accept. Some of these disadvantages are mentioned hereinfter, but these do not comprise all.
The use of a large number of magnets to achieve a rack and pinion effect is not capable of being applied to the construction of most instruments. There is insufficient space, the weight increase cannot be tolerated, one and/or the other of the moving members (driving or driven) cannot accommodate or furnish the movement needed.
The achievement of a relationship between the driving and the driven magnetic parts is not likely to or has not been achieved with a result that scales of instruments have to be specially calibrated and in the case of second order parameters must be crowded at one end and spread at the other.
The gap between the magnetic parts has heretofore been too small for practical utilization. Even assuming that a barrier can be placed between these relatively moving parts, the pressures which can be accommodated in a given instrument are proportional to the thickness with which the barrier can be built. Small gaps and consequently small barriers can only be accommodated in low pressure instruments.
The description of the invention which follows shows these disadvantages are overcome and enables the reader to appreciate that many advantages in addition are achieved.